This invention relates to a tire former for use in a tire building apparatus.
There has been known a tire building apparatus as shown in FIG. 4. In FIG. 4, a tire building apparatus 10 is provided with a tire former 12, a tread ring forming drum 14, and a transfer for transferring a tread ring to the tire former 12 from the tread ring forming drum 14. Specifically, cylindrical carcass plies are formed on the tire former 12 and bead wires are put on side ends of the carcass plies on the tire former 12. On the other hand, a tread ring is formed on the drum 14, and then transferred to the tire former 12 by the transfer 16. When the tread ring is positioned around the carcass plies on the tire former 12, the tire former 12 is axially contracted to deform the carcass plies into a toroidal shape. An outer surface of the toroidal carcass plies adheres an inner surface of the tread ring. In this way, a green tire is formed.
As shown in FIG. 5, the tire former 12 is conventionally provided with a center ring 20 and a pair of side rings 22 which are provided at opposite sides of the center ring 20. The side rings 22 are mounted on a drum shaft 18 and movable closer to and away from each other along an axial direction of the drum shaft 18.
The outer diameter of each side ring 22 is set such that an outer circumferential surface of the side ring 22 comes slidably in contact with an inner circumferential surface of the center ring 20. When the side rings 22 move closer to each other from the positions shown in FIG. 5. i.e., in directions of arrow in FIG. 5, they are consequently located inside the center ring 20. In this way, the tire former 12 changes from a wide drum stage shown in FIG. 5 to a narrow drum stage in which the side rings 22 are located inside the center ring 20.
More specifically, a green tire is built with the above tire building apparatus as follows. First, after carcass plies 26 are placed over the outer circumferential surface of the tire former 12 in the wide drum stage. Bead wires 30 including a bead apex 28 are placed at opposite outer ends of the carcass plies 26. Subsequently, an unillustrated bladder of a bead locking device 24 provided at an outer end of each side ring 22 is inflated, and opposite ends 32 of the carcass plies 26 are, as shown in FIG. 5, turned up to cover the bead wires 30. Thereafter, the side rings 22 are moved closer to each other to change the tire former 12 into the narrow drum stage, and air is supplied between the center ring 20 and the tire carcass, with the result that the tire carcass is expanded radially and deformed into a toroidal shape as indicated by the dotted line in FIG. 5.
In such conventional tire former 12, however, there are stepped portions A between the center ring 20 and the two side rings 22 in the initial state of the tire former 12, i.e., in the wide drum stage, as shown in FIG. 5. This because the outer diameters of the side rings 22 and the center ring 20 differ. In other words, the cylindrical carcass plies 26 are formed with annular stepped portions corresponding to the stepped portions A. This makes it difficult to form the carcass plies 26 into a shape of a uniform cylinder, for that matter, greatly influences the quality of the tire product. Further, the carcass plies 26 are normally obtained by adhering two or more different kinds of materials one on another. For instance, when two kinds of materials are adhered to form the carcass plies 26, a final tire product may be defective because air remains between these two materials due to the presence of the stepped portion A. Accordingly, it is necessary to remove the air remaining in the carcass plies 26 in a tire building process.
It will be seen that if the materials are adhered in an endless manner to form carcass plies without accompanying any stepped portions in the tire forming step, the air does not remain between these materials. This will eliminate the air removing operation which has been conducted in the conventional apparatus, and increase the working efficiency.
Also, the center ring 20 of the conventional tire former is made of a single ring-shaped member as well as the side rings 22. Accordingly, when the center ring 20 is replaced to change the width of tire former for formation of a different type of tire, it has been necessary to remove not only the center ring 20 but also one of the side rings 22 and bead locking devices coupled therewith from the drum shaft. Such replacement operation requires an exceedingly large amount of labor and time.